refactor: Use string literal types of generic builtins for type checking

[matthewfeickert]

Description

Resolves #1941

• Use string literal types of generic builtins for type checking until Python 3.8 support is dropped (so pyhf is Python 3.9+ only) to avoid having to check for if typing.TYPE_CHECKING.
  • c.f. https://mypy.readthedocs.io/en/stable/runtime_troubles.html#string-literal-types
  • c.f. https://mypy.readthedocs.io/en/stable/builtin_types.html#generic-types
  • c.f. https://mypy.readthedocs.io/en/stable/runtime_troubles.html#generic-builtins
  • c.f. https://peps.python.org/pep-0585/
• Remove .coveragerc as no longer needed.
  • Reverts PR test: Ignore TYPE_CHECKING for coverage #1937

Thanks @henryiii for the nudge on this.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Use string literal types of generic builtins for type checking until Python
  3.8 support is dropped (so pyhf is Python 3.9+ only) to avoid having to
  check for `if typing.TYPE_CHECKING`.
   - c.f. https://mypy.readthedocs.io/en/stable/runtime_troubles.html#string-literal-types
   - c.f. https://mypy.readthedocs.io/en/stable/builtin_types.html#generic-types
   - c.f. https://mypy.readthedocs.io/en/stable/runtime_troubles.html#generic-builtins
   - c.f. https://peps.python.org/pep-0585/
* Remove .coveragerc as no longer needed.
   - Reverts PR #1937

[matthewfeickert]

I didn't do a good job of describing the details in the PR body, so we should make this more clear before merging and rename the PR to something more correct.

[codecov]

Codecov Report

Merging #1942 (9b52d3d) into master (6f8d87e) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1942   +/-   ##
=======================================
  Coverage   98.26%   98.26%           
=======================================
  Files          69       69           
  Lines        4439     4439           
  Branches      748      748           
=======================================
  Hits         4362     4362           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	25.81% <0.00%> (ø)
doctest	61.02% <100.00%> (ø)
unittests-3.10	96.14% <100.00%> (ø)
unittests-3.7	96.13% <100.00%> (ø)
unittests-3.8	96.17% <100.00%> (ø)
unittests-3.9	96.19% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/pyhf/typing.py	100.00% <100.00%> (ø)

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